Frequency changer



y 1947. H. M. HUGE 2,424,236

FREQUENCY CHANGER Filed Bay 6, 1943 M on T I, Patented July 22, 1947FREQUENCY CHANGER Henry M. Huge, Lorain, Ohio, assignor, by mesneassignments, to Lorain Products Corporation, Lorain, Ohio, a corporationof Ohio Application May 6, 1943, Serial No. 485,831

This invention .relates to frequency changers and in particular to amagnetic frequency divider which does not require a starting transient.

The invention makes use of the saturation of a ferromagnetic core todivide the frequency of an alternating current source, and comprises abiased saturable inductance in series with a capacitor in aself-starting circuit. By my invention I am able to reduce the number ofelements required in a self-starting frequency divider and at the sametime obtain maximum efficiency, greatly improved stability withfluctuations of input voltage and load, and excellent regulation of theoutput voltage. In my frequency changer the oscil lation are stabilizedby controlling the phase relationship between the subharmonic and inputfrequency voltages across the saturable inductance, and in this mannerthe correct value of negative resistance necessary under any loadcondition is produced while maintaining a substantially constantsubharmonic voltage across the load. Another feature of my inventionprovides automatic adjustment of the biasing current to greatly extendthe usable range of input voltage ove'r which the frequency changer willoperate.

It is an object of this invention to divide the frequency of analternating current source by magnetic means. k

Another object of this invention is to provide a magnetic frequencyreducer which is self-starting without a starting transient.

A further object of this invention is to generate even subharmonics ofan alternating current source in a static frequency changer,

An additional object of this invention is to energize the biasingrectifier with voltage from the saturable inductance for which itprovides the bias.

Another object of this invention is to energize the biasing rectifier ina frequency divider with a combination of voltage from the alternatingcurrent source and voltage from the saturable inductance for which itprovides the bias.

It is also an object of this invention to supply a load with asubstantially constant subharmonic voltage in spite of variations of thealternating supply voltage or load variations.

A further object of this invention is to stabilize the operation of amagnetic frequency reducer over a, wide range of input voltage and load.

Another object of this invention is to utilize a linear inductance toincrease the operating range and stability of a frequency changer.

Another object of this invention is to provide a frequency reducerhaving a high efficiency.

18 Claims. (Cl. 172-281) Another object of this invention is to providea frequency reducer which is self-starting under normal loads andself-protecting against overloads.

Another object of my invention is to provide automatic adjustment of thebiasingcurrent supplied to the saturable inductance to compensate forinput voltage variation.

Further objects and a better understanding of my invention may be had byreferring to the following specifications and claims, in connection withthe accompanying drawings in which Figure 1 is a circuit diagram of anembodiment of my invention including a direct current source to bias thesaturable inductance,

Figure 2 is a modification of the circuit of Figure 1; in which thedirect current circuit i insulated from the alternating current circuit,and an alternative method of stabilization is shown.

Figure 3 is another modification of the circuit of Figure 1, using ahalf-wave rectifier to supply the biasing current and showing analternative method of connecting load.

Figure 4 is a circuit diagram of a preferred embodiment of my invention,showing the bias supplied by a full-wave rectifier and includingprovision for introducing harmonics in,the output voltage.

In general my invention provides new and improved means for stabilizingsubharmonic oscillations under wide variations of load and inputvoltage, for increasing the efficiency of conversion and for initiatingthe oscillations.

Referring now to Figure 1, there is shown the circuit diagram of afrequency changer made in accordance with my invention and comprising acapacitor It, a saturable inductance l3, and a filter inductance l2. Thecircuit is energized by alternating current source l0 and direct currentsource II and supplies voltage of the new frequency to the load shownconnected across capacitor I4.

Direct current from source I l flows through inductance l2 andinductance l3 and is blocked from source ID by the D. C. resistance ofthe load.

I prefer to construct the magnetic circuit of inductance I2 with asuitable air gap to avoid excessive magnetization of the core by thedirect current flowing through the winding. Saturable inductance i3 isnormally constructed with a closed magnetic circuit, thus it has anon-linear magnetization characteristic and may be referred produces anasymmetrical flux condition in inductance i3 and produces in cooperationwith capacitor I4, negative resistance at the subharmonic frequency, andwhen this negative resistance exceeds the positive circuit resistance,subharmonic oscillations start spontaneously. The subharmonicoscillations are produced most readily at a frequency which is one halfthe frequency of source 10, and the operation described in thesespecifications is primarily applicable to frequency halving, but othereven subharmonic frequencies, such as one-fourth or one-sixth the sourcefrequency can be obtained by altering the circuit constants. Generallythe wave shape of the voltages produced at these lower frequencies isnot as good as that of the voltage produced at half the sourcefrequency.

I prefer to construct inductance l2 with an impedance value whichproduces an appreciable subharmonic current flow through it. In this wayinductance 12 can be used to stabilize the oscillations over a widerange of input voltages from source in. The value of inductance I2 isset to provide optimum tuning of the circuit to both the subharmonicfrequency and the frequency of source 10. The stabilization can beaccomplished alternatively by providing the magnetic circuit ofinductance 13 with a suitable air gap in part or all of the laminationstack, thus reducing its maximum impedance value. Even with this airgap, however, inductance l3 has a non-linear characteristic. In thealternating current circuit, inductance i2 is in parallel withinductance i3 and increasing the exciting current of inductance 13produces an effect similar to that produced by increasing the excitingcurrent of inductance l2.

In the operation of the frequency changer of my invention, I am able toobtain a highly desirable load-carrying characteristic, depending on thecooperation of stabilizing inductance l2 with capacitor i4 and saturableinductance [3. When a light resistive load is applied in the circuit ofFigure 1, the voltage across capacitor i4 drops slightly, and as theloadresistance is decreased, the load voltage drops very slowly untilpeak load is approached. As the load resistance is diminished below thevalue which draws peak power, the subharmonic output voltage fallsrapidly although no instability or shift in frequency occurs at anyvalue of load. At a relatively low value of load resistance thesubharmonic oscillations cease, but a slight increase in load resistanceabove this value causes the oscillations to restart.

I have found that by controlling the phase shift between the subharmonicand fundamental voltagesacross saturable inductance i3 I can maintain anegative resistance equal to the positive resistance which changes withload. I make use of this discovery by proportioning saturable inductancei3, linear inductance i2, and capacitor M to produce a phase shiftbetween fundamental and subharmonic voltages to produce the necessarilylarge changes in negative resistance without large changes in themagnitude of the voltage across the saturable inductance. This featureof the invention gives my frequency changer a highly desirablecharacteristic so that normal variations in load do not produce largechanges in output voltage.

In the circuit of Figure 2, primary winding 33 of transformer 32 isconnected in parallel with capacitor i4 and saturable inductance 28 isprovided with two windings, winding 29 connected to alternating currentsource Ill and winding 30 connected to direct current source H.

The operation of. the frequency changer of Figure 2 is similar to thatof the frequency changer of Figure 1. The direct current supply isisolated from the alternating current supply, however, and the load isisolated from both the D. C. and A. C. sources. Furthermore, the circuitof Figure 1 is not adapted to supply a load having low direct currentresistance, whereas no such restrictions need be placed on the characterof the load in Figure 2.

Inductance 3i in Figure 2 may be increased to a value as large asdesired because the stabilizing effect can be produced by designingtransformer 32 with the correct exciting current necessary forstabilization. To accomplish this, I prefer to construct the core oftransformer 32 with a suitable air gap so that it effectively becomes alinear inductance in parallel with capacitor II.

The primary winding 33 of transformer 32 can properly be called astabilizing inductance when the word inductance is suitably defined. Theterm inductance" as used herein, does not exclude the possible use ofthe inductance windings as a transformer, but indicates that the actionof the element depends on its exciting current. This contrasts with theterm transfornn er which ordinarily implies that the exciting current ismerely incidental to the function of the element.

In the subharmonic circuit, considering saturable inductance 28 as thesubharmonic generator, inductance 3|, capacitor 14 and primary winding33 of transformer 32 are all effectively in parallel with each other.This statement is, of course, based on the assumption of negligibleimpedance in source It). This assumption is usually justified,particularly when source I0 is the commercial power supply. Under thiscondition it is easily seen that increasing the exciting current oftransformer 32 has the same effect on the subharmonic current asincreasing the exciting current of inductance 3|. The eiIect on thecurrent of the frequency of source in is not exactly same, however, andthe interchangeability of the two methods of stabilization is somewhatlimited by this fact. While I have shown the stabilizing inductance asincorporated in transformer 32, it should be pointed out that astabilizing inductance not shown may be shunted across condenser 14without making use of any transformer action if the proper value ofcapacitor I4 is selected.

An advantage of the arrangement of Figure '2 lies in the possibility ofincreasing inductance 3! to the point where it allows very littlealternating current to pass through direct current source H. Such anadjustment is advantageous for example, when source II is a telephonetalking battery.

In Figure 2 output winding 34 is insulated from both the alternatingcurrent source In and the direct current source H and can be constructedto supply any desired output voltage to the load.

Figure 2 also shows primary winding 33 tapped as an autotransformer tostep up the voltage on capacitor II. This sometimes effects an economyin permitting the use of a smaller high voltage capacitor instead of thelarge low voltage capacitor otherwise required.

The chief structural difference between the circuit of Figure 3 and thatof Figure l is the substitution of half-wave rectifier I! in Figure 3for the direct current source I I in Figure 1.

ing current flow through inductance l2 and thehalf-wave rectifier l5,and the oscillations start as a result of the superposition of thedirect and alternating currents producing an asymmetrical flux conditionin saturable inductance I3 as explained in connection with Figure 1.When the oscillations are started, however, the subharmonic currentthrough inductance l2 and rectifier l5 predominates and the biasingcurrent is chiefly rectified subharmonic current. As a result of thisfact, an additional regulating effect besides that explained inconnection with Figure 1 can be obtained, When the subharmonic voltagetends to rise, the increase in biasing current increases the saturationof inductance l3 and as a result, tends to hold the voltage down to itsnormal level. When the voltage falls, the reverse effect is observed.However, when the load is heavy enough a oint is sometimes reached whereincreasing the direct current bias increases the voltage and decreasingthe bias decreases the voltage. Under this condition overloads arelikely to greatly de- I is overcome in the circuit of Figure 4.

In Figure 3, the output winding 25 added to inductance I3 provides asimple means for insulating the load from the alternating current supplyand for keeping direct current away from the load.

The voltage supplied to the load across winding has a higher harmoniccontent than when the load is supplied by the Voltage across capacitorll, but in many cases this may not be objection able.

The circuit of Figure 4 represents the preferred embodiment of myinvention, and shows a frequency changer in which the bias for thesaturable transformer 22 is provided by a full-wave rectifier bridge 20supplied with alternating current for winding ll! of transformer l9.

Fundamentally, the operation of the frequency changer of Figure 4 is thesame as that of the frequency changers of Figures 1, 2, and 3.Alternating current is supplied from source ID to primary winding it; oftransformer l9, and from secondary winding I8 to the rectifier bridge20. Direct current from the bridge 20 is fed through inductance l2 andis superimposed on alternating current from source In in primary winding23 of saturable transformer 22.

operation with capacitor l4 produces a negative resistance to thesubharmonic current and oscillations start. The oscillations build up toa value determined chiefly by the size of capacitor As a result of thisdouble magnetization, transformer 22 in oo- H, the exciting current ofinductance l2 and the and the current supplied from winding I8 isinsufficient to maintain normal bias. In this case the self-adiustingbiasing action obtained by the rectification of subharmonic current isparticularly advantageous. By properl proportioning saturabletransformer 23, capacitor l4 and inductance I2, I am actually able tocause the sub harmonic voltage generated across capacitor ll to increasewith decreases in the voltage of source III. "This action is not fullyunderstood but it may be that reducing the voltage of source HIincreases the. impedance of winding 1 23 of transformer 22, both as aresult of reduced voltage on winding i8 and reduced voltage of thesource frequency across winding 23, and that the higher impedance ofwinding 23 causes a higher subharmonic voltage to be developed acrossit.

Capacitor 2| is not essential to the operation of the frequency changer,but several advantages are gained through its use. It decidedly reducesthe peak inverse voltage which must be sustained by the rectifier bridge20; at the same time its size may be adjusted as a control on theproportion of the subharmonic current flowing through inductance l2which is to be rectified. Increasing capacitor 2| by-passes more of thesubharmonic current around the rectifiers. Thus, the size of capacitor2| has an effect on the output voltage regulation characteristic of thefrequency changer.

The load in Figure 4 is supplied with voltage from winding 24 ofsaturable transformer 22. As explained in connection with Figure 3, thevoltage across the saturable transformer includes a component of thefrequency of source l0 and in order to balance the larger part of thiscomponent out of the output voltage, winding 24 is connected in serieswith winding I! of transformer I9. The turns on winding I! arepreferably proportioned to minimize the component of the frequency ofsource ID in the output voltage.

As .in the circuit of Figure l, inductance l2 passes subharmonic currentand acts as a stabilizing unit. At the same time, the combination ofinductance l2 capacitor l4 and saturable transformer 22 cooperate toproduce the correct phase relationship between the subharmonic voltageand the voltage of the frequency of source I0 under varying conditionsof load and input voltage to maintain the negative resistance producedin saturable transformer 22 equal to the positive circuit resistancewithout causing large changes in the subharmonic voltage supplied to theload.

When an extraordinarily heavy overload is applied, the oscillations canbe stopped, but in the preferred embodiment of my invention, theoscillations restart when the load impedance is increased only slightlyabove the value at which the oscillations ceased.

.Saturable inductance 26 and capacitor 21 are not essential to theoperation of my frequency change;- where a substantially sinusoidal loadvoltage is required. Where the voltage is used as a telephone ringingvoltage, however, it is usually desirable to provide a small percentageof high harmonics in the output voltage to serve as audible ringingtone. For this purpose, the relatively small saturable inductance 26 inparallel with the capacitor 21 generates an oscillation of a mediumaudio frequency which appears in the output, as an audible tone. Bykeeping saturable inductance 26 relatively small and saturating ithighly, I am able to minimize its influence at the subharmonic frequencyand yet to provide adequate audible tone in the output voltage.Capacitor 21 accentuates the desired audio frequency component generatedby saturable inductance 26.

In order to make the most efficient use of the units, I prefer tosuperimpose the direct current on the same winding as that carrying thealternating current, as shown in Figure 4. This necessitates usingcapacitor H as a. blocking condenser for the direct current, so nostep-up transformer is used in connection with capacitor ll as was donein Figure 2.

It will be apparent to those skilled in the art that many modificationsin the arrangement of the parts can be made without departing from thetrue scope of my invention as hereinafter claimed.

I claim as my invention:

1. A self-starting frequency divider comprising in combination a sourceof alternating current, a source of direct current, a saturableinductance, a substantially linear inductance, a capacitor, firstcircuit means connecting said saturable inductance in series with thecapacitor and the source of alternating current, and second circuitmeans connecting said saturable inductance in series with thesubstantially linear inductance and the source of direct current, thedirect current from said source producing an asymmetrical flux conditionin the saturable inductance which causes the saturable inductance incooperation with the capacitor to self-start oscillations of the dividedfrequency.

2. A self-starting subharmonic generator adapted to be energized from asource of alternating current, comprising in combination, a capacitorand a saturable inductance connected in series circuit relationship witheach other and with said source of alternating current, biasing meansproducing an asymmetrical flux condition in said saturable inductancewhich causes the saturable inductance in cooperation with the capacitorto self-start sub-harmonic oscillations, and output means supplying aload with subharmonic voltage.

3. A self-starting subharmonic generator adapted to. be energized from asource of alternating current, comprising in combination, a capacitorand a saturable inductance connected in series circuit relationship witheach other and with said source of alternating current, biasing meansproducing an asymmetrical flux condition in said saturable inductance,and output means for supplying a load with subharmonic voltage, andcircuit means causing said biasing means to respond to changes in thesubharmonic voltage to control the voltage delivered by said outputmeans.

4. A self-starting frequency divider comprising in combination a sourceof alternating current, a source of direct current, a saturableinductance, a substantially linear inductance, a capacitor, firstcircuit means connecting said saturable inductance in series with thecapacitor and the source of alternating current, and second circuitmeans connecting said saturable inductance in series with thesubstantially linear inductance and the source of direct current, andthird circuit means connecting a load substantially in parallel withsaid capacitor.

5. A self-starting frequency divider comprising in combination a sourceof alternating current, a source of direct current, a saturableinductance, a substantially linear inductance, a. capacitor, firstcircuit means connecting said saturable inductance in series with thecapacitor and the source of alternating current, and second circuitmeans connecting said saturable inductance in series with thesubstantially linear inductance and the source of direct current, andthird circuit means connecting a load substantially in parallel withsaid saturable inductance.

6. A self-starting magnetic frequency changer adapted to be energizedfrom a source of alternating current and to supply a load with voltageof a frequency one-hair the frequency of said source, comprising incombination, a saturable inductance, a capacitor, a substantially linearinductance, and a rectifier, first circuit means connecting saidsaturable inductance in series with said capacitor and said source ofalternating current, and second circuit mean carrying direct currentfrom said rectifier through said linear inductance and'said saturableinductance in ser es.

'7. A frequency changer adapted to be'energized from a sourceofalternating current, and to supply a load with voltage of a frequencywhich is an even subharmonic of the frequency of said source comprisingin combination a saturable inductance, a capacitor, biasing meansproducing a unidirectional flux in said saturable inductance, firstcircuit means connecting said saturable inductance in series with saidcapacitor and the source of alternating current, said saturableinductance, capacitor, and biasing means cooperating to produce inresponse to a change in the resistance of the load, a shift in phasebetween the voltage of the frequency of said source and the voltage ofthe subharmonic frequency across said saturable inductance to maintainoperation under variable loads with only slight changes in outputvoltage.

8. A frequency changer adapted to be energized from a source ofalternating current and to supply a load with alternating current havinga component of a frequency which is an even subharmonic of the frequencyof said source comprising in combination, saturable magnetic core means,capacitive means, biasing means producing a unidirectional flux in saidsaturable magnetic core means, winding means on said saturable magneticcore means, and circuit means connecting said winding means in serieswith the capacitive means and said source of alternating current, outputcircuit means for connecting a load substantially in parallel with saidcapacitive means.

9. A self-starting magnetic frequency divider comprising in combinationa saturable inductance, a substantially linear inductance, a capacitor,and biasing means producing an unsymmetrical flux condition in saidsaturable inductance, said saturable inductance and capacitor beingarranged in a series circuit, said linear inductance being arranged inparallel circuit relationship with said saturable inductance, outputcircuit means supplyin voltage of the divided frequency to a load.

10. A self-starting subharmonic generator adapted to be energized by asource of alternating current, comprising in combination a saturableinductance having a laminated ferromagnetic core, a capacitor, biasingmeans producing unidirectional flux in said ferromagnetic core, circuitmeans connecting said saturable inductance in series with said capacitorand the source of alternating current, producing a series circuit forsubharmonic oscillations, means for stabilizing the subharmonicoscillations consisting of an air gap in at least a portion of theiaminations in said laminated ferromagnetic core.

11. A self-starting subharmonic generator adapted to be energized from asource of alter-,

first capacitor and the source of alternating cur-' rent, second circuitmeans connecting said rectifier in parallel with said second capacitorand in series with the substantially linear inductance and thenon-linear inductance, third circuit means adapted to supply voltagefrom said source to said full-wave rectifier, and fourth circuit meansadapted to supply a load with a voltage which is the sum of voltage fromsaid saturable inductance and voltage from said source of alternatingcurrent.

12. A self-starting frequency divider adapted to be energized by asource of alternating current. comprising in combination, a non-linearinductance, a substantially linear inductance, a capacitor, a full-waverectifier, first circuit means connecting said non-linear inductance inseries with said capacitor and the source of alternating current, secondcircuit means connecting said rec-' tifier in series with thesubstantially linear inductance and the non-linear inductance, thirdcircuit means adapted to supply voltage from said source to saidfull-wave rectifier, and fourth circuit means adapted to supply a loadwith a voltage which is the sum of voltage from said nonlinearinductance and voltage from said source of alternating current.

13. A magnetic frequency changer adapted to be energized by a source ofalternating current. comprising in combination, a first, a second, and athird inductance, a capacitor, a source of direct current, said firstinductance having a saturable magnetic core, first circuit meansconnectin said first inductance in series with said capacitor and saidsource of alternating current, second circuit means connecting saidsource of direct current in series with said first inductance and saidsecond inductance and third circuit means connecting said thirdinductance substantially in parallel with said capacitor.

14. A frequency changer adapted to be energized by a source ofalternating currentand to supply a load with power at a frequency lowerthan the frequency of said source, comprising in combination, asaturable inductance, a substantially linear inductance, a capacitor, arectifier, first circuit means connecting said saturable inductance inseries with the capacitor and the source of alternating current, secondcircuit means connecting said linear inductance in series with thesaturable inductance and the rectifier. said rectifier being energizedwith subharmonic voltage and with voltage of the frequency of saidsource and providing direct current bias for said saturable inductance.

15. A self -starting frequency divider adapted to be energized by asource of alternating current,

comprising in combination, a first non-linear inductance. asubstantially linear inductance, a first capacitor. a full-waverectifier. first circuit means connecting said non-linear inductance inseries with said capacitor and the source of alternating current, secondcircuit means connecting said rectifier in series with the substantiallylinear inductance and the first non-linear inductance, third circuitmeans adapted to supply voltage from said source to said full-waverectifier, fourth circuit means adapted to supply a load with a voltagewhich is the sum of voltage from said first non-linear inductance andvoltage from said source of alternating current and means forintroducing harmonics into said load voltage, comprising a secondnon-linear inductance in series with said first capacitor and a secondcapacitor in parallel with said second non-linear inductance.

16. A self-starting subharmonic generator adapted to be energized from asource of alternating current, comprising in combination, a nonlinearinductance, a substantially linear inductance, a first capacitor, asecond capacitor, a fullwave rectifier, first circuit means connectingsaid non-linear inductance in series with said first capacitor and thesource of alternating current, second circuit means connecting saidrectifier in parallel with said second capacitor and in series with thesubstantially linear inductance and the non-linear inductance, thirdcircuit means adapted to supply voltage from said source to saidfullwave rectifier, and output circuit means adapted to supply currentof a reduced frequency to a load.

17. A self-starting subharmonic generator adapted to be energized from asource of alternating current, comprising in combination, a capacitorand a saturable inductance connected in series circuit relationship witheach other and with said source of alternating current, biasing meainsincluding a rectifier for producing an asymmetrical fiux condition insaid saturable inductance, and output means for supplying a load withsubharmonic voltage, and circuit means causing said biasing means torespond to changes in the subharmonic voltage to stabilize the voltagedelivered by said output means.

18. A frequency charger adapted to be energized by a source ofalternating current and to supply a load with power at a frequency lowerthan the frequency of said source, comprising in combination, asaturable inductance, a substantially linear inductance, a capacitor, a.rectifier, first circuit means connecting said saturable inductance inseries with the capacitor andthe source of alternating current, secondcircuit 3 means connecting said linear inductance in series with thesaturable inductance and the rectifier, said rectifier being energizedwith voltage of the frequency of said source and providing directcurrent bias for said saturable inductance.

HENRY M. HUGE.

REFERENCES CITED The following references are of record in the I file ofthis patent:

